Process of wet spinning polyvinyl alcohol



yMay 1, 1962 TETsuRo osUGl ETAL. 3,032,385

PROCESS oF WET SPINNING POLYVINYL ALCOHOL Filed April 3, 1959 INVENTORS TETSURO OSUGI KENICHI TANABE BYTAKAN! MOCHIZUKI ATTORNEY United States 3,032,385 Patented May 1, 1962 3,032,385 PROCESS F WET SPINNING PLYVINYL ALCOHOL h Tetsuro Osugi, Kenichi Tanabe, and Takani Moclnzuki, Kurashiki City, Japan, assignors of one-fourth to Air Reduction Company, Incorporated, New York, N.Y., a corporation of New York, and three-fourths to Kurashiki Rayon Co., Ltd., Okayanla Prefecture, Japan, a corporation of Japan Filed Apr. 3, 1959, Ser. No. 803,851 Claims priority, application Japan Apr. 12, 1958 6 Claims. (Cl. 18--54) This invention relates to the manufacture of synthetic filaments. More particularly, this invention pertains to a novel method for producing synthetic fibers of the polyvinyl alcohol type which have improved mechanical properties, and to a novel apparatus for carrying out the process.

Synthetic filaments of the polyvinyl alcohol type are usually formed by extruding a solution of the synthetic filament-forming material through small holes in a spinning jet into a liquid wherein the fine streams of eX- truded solution coagulate or solidify to form filaments. A widely used spinning method for spinning polyvinyl alcohol filaments is described, for example, in U.S. Patent 2,642,333, and copending application Serial No. 336,166

0f Tomonari et al., filed February 10, 1953, and now Patent No. 2,988,802. In these processes the polyvinyl alcohol solution is extruded into an up-flowing column of a coagulating liquid having a higher specific gravity than the polyvinyl alcohol solution, thus imparting to the coagulating column and polyvinyl alcohol solution a parallel upward direction of fiow without turbulence. The parallel flow is maintained until the polyvinyl alcohol coagulates into filaments. The diameter of the column is subsequently reduced, thereby increasing the rate of flow, and stretching the coagulated filaments by the combined effect of the increased rate of flow and the uplift of the filaments in the ,coagulating liquid.

Increasing the temperature of the coagulating bath is known to substantially improve the mechanical properties of the fibers produced. Unfortunately, however, when higher temperatures are used in the coagulating bath, adhesion of the filaments occurs when the fibers are taken out of the bath and wound up. For example, when the spinning was carried out at 80 C. in a coagulating bath containing less than 25% by weight of Glaubers salt, less than 35% by weight of ammonium sulfate, and less than 18% by vweight of sodium carbonate, the fibers adhered with each other after being taken out of the coagulating bath. The fiber bundles, after being roller-stretched 300% by the usual method and dried by heating, were seen to adhere to each other by inspection of a cross section under the microscope. Moreover, the tensile strengths of the resulting fibers decreased as the bath temperature increased. The tensile strengths of the fibers produced by using bath temperatures of 25 C., 50 C. and 80 C. were found to be 4.3, 3.6 and 2.3 grams per denier respectively. Similar results were obtained when the spinning was carried out using a coagulating bath containing 20% by weight of Glaubers salt at 60 C. Therefore, spinning methods which merely use a higher temperature for the coagulating salt bath are unsatisfactory, in that any advantages which are'obtained in improved mechanical properties of the fibers, are lost dueto the later adhesion of the fibers when they leave the coagulating bath under the high temperature conditions. Moreover the mechanical advantages may later be lost in the course of stretching the fibers.

A vprincipal object of this invention is to provide a flthod .fOl-Pfolllclng .POIYVUYLBlCOhQlfilaments having the improved physical properties which are brought about by the use of higher temperatures in the coagulating bath, without adhesion of the fibers with one another after leaving the coagulating bath, and without loss of valuable mechanical properties on stretching.

Another object of the invention is to provide a polyvinyl alcohol fiber having improved physical characteristies and being suitable as a synthetic fiber for the manufacture of textiles.

Other objects and advantages of the invention will be apparent from a consideration of the specification and claims.

The attached drawing illustrates a spinning apparatus useful in the invention.

According to the present invention, a solution of the filament-forming material is extruded in the form of fine streams into a coagulating liquid having a temperature above 72 C. After coagulation of the fine streams of spinning solution at a temperature above 72 C. thevtemperature of the bath is lowered to below 58 C. before exit therefrom of the coagulated filaments in order to prevent later adhesion of the filaments and possible loss of valuable mechanical properties on stretching.

In a preferred practice of the invention the initial spining conditions are regulated in the manner described in U.S. Patent 2,642,333 and co-pending application Serial No. 336,166 of Tomonari et al., filed February l0, 1953. In accordance with the present invention, the upflowing column of coagulating liquid .is maintained at a temperature above 72 C. and the spinning solution is coagulated therein. Prior to departure of the coagulated filaments,l from the coagulation bath, the bath temperature is adjusted to below 58 C. to cool the filaments sufficiently such that the filaments do not adhere to each other withv resulting deterioration upon leaving the coagulating bath. The time of contact of the filaments with the coagulating bath portions at different temperatures will depend upon the bath temperatures, the speed of flow of the coagulating bath, the filament speed, thel immersion length, and the like. Improved fibers are obtained when the coagulating bath temperature is maintained above 72 C. through most of the immersion length. Temperatures up to 90 C. have been found to give excellent results. The emperature at which the filaments leave the bath is preferably kept below 58 C. Temperatures as low as 40 C. give good results.

Various means may be employed to provide that the fibers contact coagulating solution offlower temperature when leaving the bath. For example, means whereby the latter part of the coagulating solution is cooled by indirect heat exchange can be employed. Methods inv coagulating bath is introduced into the spinning apparatus' upwardly through ports 2. In the lowerzone of the spinning apparatusthe coagulating bath gradually inf creases in velocity. The extruded fine streams of spinning solution are carried upwardly and coagulated and gently stretched. In the middle zone B of the spinning apparatus the filaments are further coagulated and stretched. Enlarged zone C is provided near the top of the spinning column. Lines3 are provided for removing a part of the coagulating bath. Additional coagulating bath which is at a lower temperature is introduced into zone C through lines 4. The coagulating bath overflows at 5 and may be vcollected and reused by means not shown. Illustrative temperatures of the coagulating bath introduced through lines 2 and 4 are shown onthe drawing as well as illustrative temperatures in the different zones of the spinning apparatus. Also shown are illustrative lengths of the various sections of the spinning apparatus.

Salts to be used as the coagulating solution should have the ability to coagulate polyvinyl alcohol aqueous solution at a temperature higher than 72 C. Salts such as, for example, Glaubers salt, ammonium sulfate, potassium sulfate, zinc sulfate, magnesium sulfate, aluminum sulfate and sodium chloride may be used. The coagulating solution which iiows in at a lower temperature when the fibers leave the bath is preferably the same kind and the same concentration as the initial coagulating bath, but salts of a different kind and concentration may also be employed. Solutions of higher coagulating power and concentration bring about more favorable results.

The invention will be described in greater detail in conjunction with the following examples, which are typical, but the invention is not limited to the details thereof.

Example I Polyvinyl alcohol having a degree of polymerization of about 1700 was dissolved in water to form a spinning solution containing 15% by weight of polyvinyl alcohol. This solution was spun at 78 C. to form filaments in the vertical spinning machine illustrated in the accompanying drawing. The polyvinyl alcohol solution was extruded through aspinneret jet having 600 holes, each of 0.08 mm. diameter. The coagulating bath contained 30% by weight sodium sulfate and had an initial speed of 4 m./min. and an exit speed of 10 m./min.

The spun filaments travelled upwardly through the column where a sodium sulfate salt solution at'30 C. was supplied to the upper bath zonev as illustrated so that the resulting temperature in this part was 45 C. The filaments were then taken out of this bath.

A part ofthe filaments (the first series) was wound up and then air-dried at 230 C. The larnents were then heat-stretched 300% Within l0 seconds, and afterwards heat-treated at 235 C. for 30 seconds under constant length.

A part of the filaments (the second series) was rollerstretched 300%, dried by heating, and heat-treated at 235 C. for 30 seconds at constant length.

To illustrate the invention, the mechanical properties of the fibers so obtained were compared with fibers coagulated at 28 C., 50 C. and 60 C. bath temperatures in which there was no cooling when the filaments left the bath. These latter fibers were stretched and heattreatedin the same manner as the first series above.

The data given in the `above table for the common strength, knot strength, and elongation of the fibers obtained by spinningin high temperature bath, followed by lowering the exit temperature according to the present invention show that superior filaments are produced. Moreover, when roller-stretching was later applied no deterioration of thequality of the fiber occurred. The fibers which were wound upafter being takenout xof the bath, and subsequently air dried, heated and dried, and subjected to roller-stretching, showed no adhesion with each other, by inspection of a cross section with a microscope.

The fibers made according to this invention also have improved transparency. When the fibers are chemically acetylized by reaction with formaldehyde they will be dyed to a deeper color per unit equivalent of dyestutf used.

The reason for the better physical properties of the fibers obtained by reducing the exit temperature according to this invention is not certain but the following two experiments possibly give some explanation.

(1) Microscopic examination of the fibers produced at bath temperatures of 28 C. and 50 C. produced bright spots on the outer periphery of the fiber and this tendency was greater at 28 C. The fibers produced-at bath temperatures of 78 C. showed only dark spots. No bright spots could be observed at all. This showed that a certain change in the arrangement of the molecules occurs on coagulation at different temperatures. A higher arrangement occurs at a lower temperature, but such arrangements do not occur at all at a higher temperature.

(2) Films of an aqueous solution of polyvinyl alcohol on a glass plate were coagulated by using aqueous` solutions of 30% Glaubers salt at 25 C., 50 C. and 75 C. respectively. The films were irradiated with X-ray parallel to the surface thereof. The reiiection intensity of the X-ray at about 20 of a0 on the infra-red ray in the direction normal tothe surface of the film was examined by Geiger counter. The intensity increased with increasing coagulating bath temperature. The intensity was 0.84 for the 28 C. film and n0.97 for the 75 C. film. These results show that the plane of the polyvinyl alcohol molecular chains is parallel to the surface of the film at a low temperature coagulations and that such arrangements are few at a high temperature. Therefore, it can be assumed that at high coagulation temperature segments or molecules of polyvinyl alcohol are comparatively in a free state without restriction. Accordingly, with the fibers coagulated at a higher temperature the polyvinyl alcohol segments are in a free state, and more favorable properties are imparted to these fibers when they are later stretched.

Example 2 Polyvinyl alcohol having a degree of polymerization of about 2700 was dissolved in water to form a spinning solution containing 14% by weight of polyvinyl alcohol. The polyvinyl alcohol solution was extruded through spinnerets into an aqueous solution containing byweight 30% sodium sulfate with a coagulating bath length of 2 m. The temperature near the spinneret was 90 C., and the exit temperature was 45 C., with substantially a linear temperature gradientin-between. After leaving the bath at a speed of 30 m./min., the fibers were given continuous roller-stretch treatment of 200%. The fibers were then dried and subjected to heat treatment at constant length at 235 C. for one minute. Comparison of these fibers with those obtained under the same conditions except that the coagulating temperature was kept at a constant 45 C. temperature is shown below:

Temperature of coagulating bath 90,190 45 .-45 Strength, g./d 2; 23 1, 75 34. `32

Elongation, percentV aqueous solution 'of sodium sulfate at 35 C. was poured therein at a distance of l cm. from the exit of the coagulatng bath to give an exit bath temperature of 48 C. 'I'he bath exit speed was 5 m./min. The fiber was then roller-stretched continuously 300%, dried by an infra-red ray, and stretched further 100% for 10 seconds at 240 C. The fiber was then contracted 15% in 10 seconds at 240 C. and formalized at 50 C, for one hour in a solution containing formaldehyde, 15% sulfuric acid and 5% sodium sulfate.

The fibers obtained by the above process were compared with fibers prepared similarly wherein the zinc sulfate coagulatng bath was maintained at 45 C. temperature and Glaubers salt solution at 45 C. was added near Example 4 Polyvinyl alcohol having a degree of polymerization of about 980 was dissolved in water to form a spinning solution containing 19% by weight of polyvinyl alcohol. The polyvinyl alcohol solution was extruded through spinnerets into an aqueous solution containing 42% by weight of ammonium sulfate. The length of the coagul ating bath was 1.5 m. `and its temperature 75 C. A part of the coagulatng bath flowed out at a distance of 50 cm. from the exit ofthe bath, and a coagulatng solution at 40 C. containing 42% of ammonium sulfateby weight was poured therein. Thev temperature of the bath when the fiber left the bath was thus brought to 40 C.

The `fiber prepared as above was compared with a fiber spun in a 'bath containing 42% ammonium sulfate by weight at a constant temperature of 40 C. Both of the fibers were stretched as long as possible in 35% ammonium sulfate solution at 90 C, After drying, their Example 5 Polyvinyl alcohol having a degree of polymerization of about 1700 was dissolved in water to form a spinning solution containing 15% by weight of polyvinyl alcohol. The polyvinyl alcohol solution was extruded through a spinneret into an aqueous solution containing 30% by weight of sodium sulfate. The length of the coagulatng bath was 1.5 m. and the temperature was 78 C. An aqueous solution containing 30% by weight of Glaubers salt at a temperature of 35 C. was poured therein. The bath temperature when the liber left the bath was 53 C. Spinning was effected at a bath exit speed of 40 m./min. The fiber was roller-stretched continuously 150%, dried by an infra-red ray` and lthen wound up. The fibers thus obtained were stretched as long as possible for seconds at 245 C., and then formalized at 50 C. for one hour in a solution containing 5% formaldehyde, 15 sulfuric acid and 10% sodium sulfate.

The fibers prepared as described above were compared to fibers treated similarly to the above process in a coagulatng bath at a constant temperature at 45 C. and at a constant temperature of 78 C.

The fibers prepared by the invention had homogeneous cross section and good dyeing characteristics.

6 Example 6 l Polyvinyl alcohol solution having a degree of polymerization of about 500, which was acetalized to an acetalization degree of 30 mole percent using -cyclohexylaminobutyraldehyde, was mixed with polyvinyl alcohol having a degree of polymerization of about 2200 to have an average aminoacetalization degree in the polymer of 1%. This mixture was dissolved in water to form an aqueous spinning solution having a polymer concentration of 13%. The polyvinyl alcohol solution was extruded through a spinneret into a coagulatng bath of saturated aqueous solution of sodium sulfate, the bath having a temperature of 75 C. The immersion length was 2 m. and the exit speed 10 m./min. A saturated aqueous solution of sodium sulfate at a temperature of 35 C. was poured in at a distance of 1 m. from the exit, making the temperature of the bath 42 C. when the fiber left the bath.

The fibers thus obtained were stretched 300% for 1 minute in nitrogen at 220 C, and further heat-treated for 1 minute at constant length in water vapor at 225 C. under one atmosphere pressure. The fibers were then acetalized in an aqueous solution containing 1% benz'aldehyde, 5% sulfuric acid and 10% methanol at 60 C.

for one hour.

The fibers obtained bythe above process were compared with fibers treated similarly except that the coagulatng bath temperature was 42 C. throughout.

- We claim:

l. The method of preparing improved polyvinyl alcohol fibers which comprises forming an aqueous polyvinyl alcohol spinning solution, extruding the said spinning solution in the form of fine streams into a warm coagulatng salt solution bath having a temperature above 72 C., coagulating the said fine streams in said warm coagulatng solution to form filaments, contacting the said filaments with a cool coagulatng solution bath having a temperature lower than 58 C. substantially immediately after contact with said warm solution for a time sufficient t0 prevent subsequent adhesion of the filaments to each other upon leaving the cool coagulatng solution bath, and withdrawing the filaments from the cool coagulatng solution bath.

2. In the process for wet-spinning polyvinyl alcohol fibers by extruding tine streams of polyvinyl alcohol solution into an up-liowing column of a coagulatng liquid having a higher specific gravity than said polyvinyl alcohol solution, imparting to said coagulatng column and said fine streams of polyvinyl alcohol a parallel upward direction of How without turbulence, maintaining said unturbulent parallel flow until the polyvinyl alcohol coagulates t0 filaments, subsequently reducing the diameter of said column, thereby increasing the rate of flow thereof, and stretching said coagulated filaments by said increased rate of ow and the uplift of the filaments in the specifically heavier column of the coagulatng liquid, the improvement which comprises maintaining the up-owing column of coagulatng liquid at a temperature above 72 C. until the fine streams of polyvinyl alcohol coagulate to form filaments and subsequently reducing the temperature of the coagulatng liquid in contact with the filaments to below 58 C. to form a cool coagulatng solution bath, the contact with said cool solution being for a time sufficient to prevent adhesion of the filaments to each other upon leaving the cool coagulatng solution bath.

3. A method of preparing improved polyvinyl alcohol fibers which comprises the steps of forming an aqueous polyvinyl alcohol spinning solution, extruding said spinning solution in the form of fine streams upwardly into a warm coagulatng salt solution bath having a temperature above 72 C., coagulatingsaid fine streams in said coagulating solution to form filaments, contacting said filaments with a cool coagulating solution bath having a temperature lower than 58 C. substantially immediately after contactwth said warm solution for a time sufiicient to ,prevent subsequent adhesion of'the filaments to each other` upon leaving the cool coagulating solution bath, and withdrawing the laments from said cool coagulating solution bath.

4. A method of preparing improved polyvinyl alcohol fibers which comprises the steps of forming an aqueous polyvinyl alcohol spinning solution, extruding said spinning solution in the form Offine streams into a warm coagulating salt solution bath having a temperature of 72 to 90 C., coagulating said fine streams in said` coagulating solution at said temperature to form tilaments, contacting said filaments with a cool coagulating solution bath having a temperature of 40 to 58C. substantially immediatelyafter contact with said warm solution for a time sufiicient to preventsubsequent adhesion of the filaments to each other upon leaving the cool coagulating solution bath, and withdrawing the filaments from said cool coagulating solution bath.

-5. A methodof preparing` improvedpolyvinyl alcohol fibers which comprises'the steps of forming an aqueous polyvinyl alcohol spinning solution, extruding said spinning' solution in the form of fine streams upwardly into a Warm coagulating salt solutionbath having a temperature of 72 to 90 C., Vczoagulating said fine streams in said coagulating solution at said temperature to form filaments, contacting said filamentsl with a cool coagulating solution bath having a temperature of .40 to.58 C. substantially immediately after contact with said warm solution for a time sufiicient to prevent subsequent adhesion of the/filaments to :eachother .upon leaving the cool coagulating solution bath, and withdrawingthe filamentsffromsaid cool ooagulating solutionbath.

6. In the processffor wet-spinning polyvinyl alcohol fibers byextruding finestreams .of polyvinyl alcohol solution into an up-flowing'column of a coagulating liquid having a higher specific vgravity than said polyvinyl alcohol solution, imparting to said coagulating column and said fine streams of polyvinyl alcohol a parallel upward direction of flow without turbulence, maintaining said unturbulent parallel iiow until the polyvinyl alcohol coagulates to filaments, subsequently reducing .the diameter of said column, thereby increasing the rate of flow thereof, and stretching said coagulated filaments by said increased rate of ow and the uplift of the filaments in the specifically heavier column of the coagulating liquid, the improvement which comprises maintaining the up-iiowing column or" coagulating liquid at a temperature of '72 to 90 C. until the fine streams of polyvinyl alcohol coagulate to form filaments, andsubsequentlyreducing the temperature of thecoagulating liquid in contact with rthe filaments to 40 to 58 C. to form a coolcoagulating solution bath for a time sufficient to prevent adhesion of the ilaments to each other upon leaving the cool coagulating `solution bath.

References Cited in the.' file of this patent UNITEDSTATES PATENTS 

1. THE METHOD OF PREPARING IMPROVED POLYVINYL ALCOHOL FIBERS WHICH COMPRISES FORMING AN AQUEOUS POLYVINYL ALCOHOL SPINNING SOLUTION, EXTRUDING THE SAID SPINNING SOLUTION IN THE FORM OF FINE STREAMS INTO A WARM COAGULATING SALT SOLUTION BATH HAVING A TEMPERATURE ABOVE 72*C., COAGULATING THE SAID FINE STREAMS IN SAID WARM COAGULATING SOLUTION TO FORM FILAMENTS, CONTACTING THE SAID FILAMENTS WITH A COOL COAGULATING SOLUTION BATH HAVING A TEMPERA- 